1. Field of the Invention
The present invention relates to compositions of matter characterized by their improved dispersibility in thermoplastic resins. More particularly, the present invention relates to chemically treated inorganic pigments suitable for use in thermoplastic resins. Most particularly, the present invention relates to titanium dioxide pigments treated with an organophosphate ester treating agent.
2. Description of the Prior Art
The use of inorganic pigments such as, for example, pigmentary titanium dioxide, as UV light stabilizers, colorants, opacifiers and the like in various thermoplastic resins is known. It also is known, however, that due to the hydrophilic nature of such inorganic pigments and to the hydrophobic nature of the thermoplastic resins, the compatibility and thus the dispersibility of such pigments in such resins, particularly at high pigment loadings, leaves much to be desired.
It further is known that the compatibility and thus the dispersibility of inorganic pigments in thermoplastic resins can be significantly improved through chemical surface treatment of the pigments. For example, in U.S. Pat. No. 4,209,430 it is disclosed to treat inorganic pigments such as titanium dioxide pigment with phosphorylated polyenes, i.e., aliphatic polyunsaturated compounds of at least ten carbon atoms to which a phosphoryl group has been added to the olefinic unsaturation thereof. The pigments thus treated are described as not only possessing improved pigment properties but also improved uniformity of dispersion and a reduced tendency to yellow in those thermoplastic polyolefins to which the treated pigments may be added.
Further examples of methods or treatments for reducing the tendency of inorganic pigments, and particularly titanium dioxide, to yellow in various polymeric compositions are those disclosed in U.S. Pat. Nos. 4,357,170 and 4,377,417. According to these patents, the application to pigmentary titanium dioxide of an additive system comprised of either the combination of an organophosphate/alkanolamine addition product and a polyol or the organophosphate/alkanolamine addition product alone results in a reduction of the tendency of titanium dioxide pigment to yellow in polymeric compositions. The organophosphate materials utilized to produce the addition product include those organophosphate materials disclosed in U.S. Patent No. 3,380,927. These materials comprise orthophosphate or polyphosphate coesters of, conjointly, an aliphatic alcohol containing 6 to 16 carbon atoms and a nonionic adduct of ethylene oxide and a reactive hydrogen containing organic compound. The organic compounds employed to form the adduct include alkylated phenols, aliphatic alcohols containing 6 to 25 carbon atoms, aliphatic monocarboxylic acids and the like. Neither U.S. Pat. No. 4,357,170 nor U.S. Pat. No. 4,377,417 mentions any benefit to be afforded by such treatment relevant to the dispersibility of the thus treated pigment when employed in a polymeric composition.
A still further example of the treatment of inorganic fillers or pigments with organophosphate esters is found in U.S. Pat. No. 4,183,843. This patent teaches the surface treatment of inorganic fillers or pigments, including titanium dioxide, with polar phosphate ester surfactants containing both acid and polar ether groups. The thus treated fillers or pigments, when combined with a sprayable, curable polyester resin results in filler or pigment/polyester dispersions of reduced viscosities. Although the exact nature or structure of the treating materials is not definitively identified, materials such as Triton QS-44, a product of Rohm and Haas, listed as an exemplary coating material is known to comprise the composition, octylphenoxyethoxyethylphosphate.
None of the foregoing patents suggest either the treated inorganic pigments or the polymeric concentrates produced therefrom which are the subject of this application.